A piezoelectric power-generating device is known as a power-generating device that applies mechanical energy, such as acceleration or distortion externally, to an element made of piezoelectric material, so that the mechanical energy is converted to electric energy by piezoelectric effect. Use of electric power generated by this piezoelectric power-generating device to a variety of sensors or a power supply for a low-power wireless communication eliminates wirings and batteries. This is called as “energy harvesting technique”, which has been eagerly developed in recent years.
FIG. 11 is a side view of piezoelectric power generating device 500 disclosed in PTL 1. Piezoelectric power generating device 500 includes metal vibrating plate 502 and piezoelectric transducer vibrator 501 including piezoelectric board 503 fixed to a main surface of metal vibration plate 502. A root portion of piezoelectric transducer vibrator 501 is fixed to a fixing portion, such as a housing.
Piezoelectric power generating device 500 further includes magnet 505 mounted to a free end of vibrator 501, and movable element 506. An operator moves movable element 506 along direction D500 to cause vibrator 501 to deform due to an attractive force of magnet 505. When a restoring force of deforming vibrator 501 becomes larger than the attractive force, the attracting is released. Vibrator 501 then generates a resonant vibration. The resonant vibration transmits to piezoelectric board 503 and is converted into electric energy, thereby generating electric power.
PTL 1 does not disclose a material of piezoelectric board 503. PTL 2 discloses lead-ZIRCONATE-TITANTE-based piezoelectric ceramics as a preferable material of piezoelectric board 503 having a large piezoelectric constant.
Larger widths of piezoelectric transducer vibrator 501 and piezoelectric board 503 allow piezoelectric power generating device 500 to generate larger electric power; however, this structure is not preferable since it enlarges the total dimensions of piezoelectric power generating device 500.
A larger attractive force of each of magnet 505 and movable element 506 increase a displacement amount of vibrator 501, thereby allowing power generating device 500 to generate larger electric power; however, this structure needs to apply a large force to piezoelectric board 503. In the case that piezoelectric board 503 is made of a piezoelectric ceramic material, a fragile material, the above structure may produce cracks on board 503 during operation, so that a decrease in electric power energy can be invited. When piezoelectric power generating device 500 is used as an energy-harvester for eliminating batteries and wirings, it is crucial to acquire a long-term reliability.
PTL 2 discloses a piezoelectric power generating device in which only compressive stress is applied to a piezoelectric since piezoelectric ceramic material has a smaller rigidity to tensile stress than to compressive stress.